In the following, reference will be at times made to prior art documents, the full particulars of which is to be found at the end of the description before the claims.
Myxobacteria are Gram-negative, rod-shaped bacteria commonly found in soil and decay vegetation (Kaiser et al., 1979). Myxobacteria are generally a rich source of antibacterial agents, that exhibit a wide range of chemical structures, mode of action and anti-microbial spectrum (Rosenberg and Varon, 1984). One strain, M. xanthus TA, produces a broad spectrum antibacterial agent when grown under nutritionally limited conditions, during the end of its exponential growth phase. This antibacterial agent which is disclosed in Rosenberg, U.S. Pat. No. 3,973,005 was termed "TA", and is capable of inhibiting growth of a variety of Gram-positive and Gram-negative bacteria (Dworkin & Kaiser, 1985; Rosenberg et al., 1973). The growth inhibition is caused by lysis of growing bacteria as a result of blocking of cell wall synthesis at the stage of polymerization of the lipid disaccharide-pentepeptide (Rosenberg et al., 1973; Zafriri et al., 1981).
TA is a molecule with a molecular weight of 623.8 dalton, and having the molecular formula C.sub.34 H.sub.57 O.sub.9 N (Rosenberg et al., 1982; see FIG. 1 for its structure). TA binds tightly to a variety of tissues and surfaces and retains its activity while in the bound form (Manor et al., 1985; Rosenberg et al., 1984). For example, TA binds to dental hard and soft tissues, which allowed the use of this antibiotic to treat severe gingivitis and to reduce plaque in humans (Manor et al., 1989). One of the disadvantages of the TA antibiotic is that it loses its activity following simultaneous exposure to air and light (Rosenberg et al., 1982). An antibiotic drug showing some of the beneficial properties of TA antibiotics but being stable to such exposure, will be highly desirable. The present invention aims at the provision of such an antibiotic drug.